HeightField doesn’t respect the active layer.
While placing it, the preview elements are fine.
The result is on layer Standard.
If the layer Standard doesn’t exist, it is created.
This is only with output as mesh.
Thank you for your report, I can reproduce this issue as well. I have logged it with our development engineers.
RH-90052 HeightField: Doesn’t respect active layer
RH-90052 is fixed in Rhino 8 Service Release 26